The objective of this project is to study the mechanism(s) of chemically induced leukemia. Our approach is focused on (1) developing in vivo model(s) in which specific types of leukemia are elicited rapidly and in high yield by chemicals in rodents, (2) utilizing these systems to characterize the alterations of the proliferation and differentiation of hemopoietic cells at different stages of leukemia in order to better define the target(s) of transformation and the sequence of cellular events which mediate the progression of neoplasia, (3) investigating the biological interactions of chemical carcinogens and tumor promoters on hemopoietic target cells in vitro, and (4) characterizing the covalent interactions of chemicals with DNA in hemopoietic tissues to gain further knowledge of the initiation stage of chemically induced leukemia. Chemicals which are under investigation include 7,12-dimethylbenz[a]anthracene (DMBA), 7,8,12-trimethylbenz[a]-anthracene (TMBA), N-methylnitrosourea (MNU), N-hydroxy-2-acetylaminophenanthrene (N-OH-AAP), N-acetoxy-2-acetylaminofluorene (N-OAc-AAF), and 12-O-tetradecanoyl-phorbol-13-acetate (TPA). Results obtained so far are (1) detection of DMBA-DNA adduct formation in bone marrow and spleen cells of rats following an i.v. dose of DMBA, (2) development of cell culture clonal assays detecting an array of rat and mouse hemopoietic progenitor cells, (3) demonstration of a stimulatory effect of TPA on monopotent and bipotent hemopoietic cells but a lack of any effect of DMBA, MNU, N-OH-AAP, and N-OAc-AAF on various progenitors in cell culture. Future studies will include (1) continuation of the development of a method to elicit erythroleukemia in rats by DMBA and TMBA, (2) characterization of the colony formation ability in cell culture of hemopoietic progenitors in DMBA and TMBA treated rodents, and (3) determination of in vivo formation of DNA adducts with TMBA in hemopoietic tissues.